1. Field of the Invention
The present invention relates to a lateral edge position detector for recording paper, and a printer. More particularly, the present invention relates to a lateral edge position detector for recording paper, and a printer, in which detection of a lateral edge of the recording paper is possible with a simple structure, and precisely and stably.
2. Description Related to the Prior Art
A digital still camera has been widely used. A user electronically photographs an image with the digital still camera, to store image data. To reproduce the image, a color printer is used, in which the image data is processed to produce a full-color print on a recording medium, such as recording paper. It has been conceivable to produce a full-width print having no blank margins on any edge of the periphery of the image. This is effective in utilizing a printing surface of the recording paper without waste.
A color thermal printer is included in the various image forming apparatuses, and capable of producing a full-color print. For the color thermal printer, color thermosensitive recording medium is used, and includes a support, and yellow, magenta and cyan thermosensitive coloring layers overlaid thereon. A thermal head or printhead includes an array of heating elements, which apply pressure and heat to the recording paper. The coloring layers are heated and colored one after another, to record a full-color image on the recording paper according to three-color frame-sequential recording.
To produce a full-width print in the color thermal printer, it is necessary to enlarge the width of the array of the heating elements over the width of the recording paper. If some of the heating elements not contacting the recording paper are driven, wasteful heat is generated. This is unfavorable because the life of the heating elements will be shortened. In view of this, there is a proposed printer which includes a CCD line sensor, and in which a lateral edge of the recording paper is detected by the CCD line sensor to determine the position of the recording paper in the main scan direction or array direction of the heating elements. The non-contact heating elements are recognized, and are kept from energisation. For example, U.S. Pat. No. 6,305,856 (corresponding to JP-A 2001-030532) discloses a printer including the CCD line sensor of which a length is greater than the width of the recording paper. Also, it is conceivable to use a small type of two CCD line sensors disposed near to lateral edges of the recording paper.
The CCD line sensor having a long shape is remarkably expensive, and is a specific cause to raise a manufacturing cost of the color thermal printer. The total number of produced articles of the CCD line sensor with the great length is somewhat low. It is considerably difficult to plan the production of the color thermal printer because of the difficulty in expecting the demand of the CCD line sensor.
The CCD line sensor with a small size, in contrast, is inexpensive, and easy to obtain. However, a portion along the lateral edge of the recording paper is likely to have a curl, so as to change a distance from the lateral edge to the CCD line sensor. The change in the distance to the recording paper causes changes in the signal level of an output of the CCD line sensor. Thus, the precision in the position detection of the recording paper will be lower. Note that it is possible to change the type of the recording paper from an ordinary type to a sticker type. If the sticker type of the recording paper is used for a long time, an adhesive component is likely to bleed out of the sticker, and deposit on the surface of the CCD line sensor. This lowers the cleanness of the detecting surface of the CCD line sensor, to lower the precision in the detection.